Diode lasers are combined with DFG (ωDFG = ω1 - ω2) in appropriate dielectric materials (e.g. Periodically poled lithium niobate, PPLN) to produce light in the mid-IR. DFG allows access to shorter wavelengths with narrow linewidths and wide, continuous tuneability. By combining DFG systems with advanced spectroscopic techniques such as cavity enhanced techniques and modulation spectroscopy, detection of trace species at a range of concentration levels (from ppm to ppt) is possible. This is useful in the analysis of human breath in order to measure abnormal levels of certain volatile organic compounds in exhaled breath, which act as biomarkers for specific diseases.
Back to Mid-IR Spectroscopy.